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Method of estimating a position of a mobile object in a navigation systemRelated Patent Categories: Data Processing: Vehicles, Navigation, And Relative Location, Navigation, Employing Position Determining Equipment, For Use In A Map Data Base System, Including Route Searching Or Determining DeviceMethod of estimating a position of a mobile object in a navigation system description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060041377, Method of estimating a position of a mobile object in a navigation system. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] Pursuant to 35 U.S.C. .sctn. 119(a), this application claims the benefit of earlier fling date and right of priority to Korean Patent Application No. 10-2004-0064538, filed on Aug. 17, 2004, the content of which is hereby incorporated by reference herein in its entirety. FIELD OF THE INVENTION [0002] The present invention is directed to a method of estimating a position of a mobile object in a navigation system that can assure an accurate estimation of a current position of a mobile object by establishing an azimuth angle of a link which the mobile object has entered, as an azimuth angle of the mobile object itself, when the current position of the mobile object has to be estimated by dead reckoning navigation due to failure of normal reception of navigation messages. BACKGROUND OF THE INVENTION [0003] These days, traffic congestion becomes aggravated due to steady increase of mobile objects such as automotive vehicles and the like. This is particularly serious in that the expanding speed of social infrastructure including roads can hardly catch up with that of the number of mobile objects. [0004] As one of the solutions to the traffic congestion, attention has been drawn to a navigation system where a Global Positioning System (GPS) receiver receives navigation messages periodically transmitted from earth-orbiting satellites for a global positioning system and sensors mounted on a mobile object detect the travel conditions, e.g., speed and heading. The navigation system is also adapted to determine a current position of the mobile object in response to the navigation messages received by the GPS receiver and the travel condition signals detected by the sensors, which in turn is matched to a map data and displayed on a display unit. [0005] Such a navigation system enables a user of a mobile object to confirm a current position of the mobile object and the shortest route to a target destination from the current position. Under the guidance of the navigation system, the user can search in advance for a travel route along which the mobile object will run to reach the target destination and then drive the mobile object along the travel route thus searched, which makes it possible for the user to efficiently utilize a given road network. [0006] At an initial stage of travel of the mobile object, which is an initial operation of the navigation system, there may occur such an instance that a navigation system fails to accurately receive the navigation messages transmitted from the GPS satellites for a period of 30 seconds minimum to 15 minutes maximum, depending on weather condition, building lay-outs around the mobile object, the solar spot and arrangement of the GPS satellites with respect to the current position of the mobile object. In the event that the navigation messages are not received accurately, the navigation system estimates the current position of the mobile object by what is called dead reckoning navigation. In other words, the navigation system can estimate a current position of the mobile object by taking advantage of the detection signals issued from a gyroscope, a vehicle speed sensor and the like, all of which are built in the mobile object. [0007] In case of estimating the current position of the mobile object by the dead reckoning navigation, an azimuth angle of the mobile object is approximately detected by integrating the detection signals of the gyroscope and then accumulating the integrated values. Estimating the azimuth angle of the mobile object by the gyroscope detection signals in this manner, however, has a limitation in accurately detecting the azimuth angle of the mobile object, because a bit of error is generated each time of estimation and continues to accumulate as the mobile object travels. [0008] In particular, due to the errors in the azimuth angle of the mobile object accumulated as the mobile object enters and continues to travel along a link of a map, there poses a drawback in that the current position of the mobile object cannot be precisely matched to the link but, instead, tends to be matched to the location that falls outside the link. SUMMARY OF THE INVENTION [0009] Accordingly, it is an object of the present invention to provide a method of estimating a position of a mobile object in a navigation system adapted to minimize errors in an azimuth angle of the mobile object and thereby assure an accurate estimation of the current position of the mobile object by way of establishing the azimuth angle of a link which the mobile object has entered as the azimuth angle of the mobile object when the current position of the mobile object is estimated by dead reckoning navigation. [0010] In accordance with one aspect of the instant invention, there is provided a method of estimating a position of a mobile object in a navigation system, comprising the steps of: loading a mobile object position data backed up during stoppage of the mobile object, at an initial stage of travel as the mobile object restarts traveling; estimating a current position of the mobile object from the loaded position data of the mobile object by dead reckoning navigation; causing the estimated current position of the mobile object to be matched to a map data; determining whether the mobile object has entered a link, based on the mobile object position matched to the map data and detection signals indicative of travel conditions of the mobile object generated from a sensor part; and estimating the current position of the mobile object by establishing the azimuth angle of the link as an azimuth angle of the mobile object through the dead reckoning navigation if the mobile object is determined to have entered the link. [0011] In accordance with another aspect of the present invention, there is provided a method of estimating a position of a mobile object in a navigation system, comprising the steps of: detecting a mobile object position through the use of navigation messages received by a GPS receiver; calculating a dilution of precision value for the position detected; and comparing the dilution of precision value with a predetermined threshold value in a control part, wherein the current position of the mobile object is estimated by the dead reckoning navigation, if the dilution of precision value is equal to or greater than the threshold value. [0012] In accordance with still another aspect of the present invention, there is provided a method of estimating a position of a mobile object in a navigation system, comprising the steps of; judging a position detected by the GPS receiver to be a current position of the mobile object if the dilution of precision value is less than the threshold value; and causing the judged position of the mobile object to match a map data. [0013] Preferably, the determining step comprises the steps of: the mobile object having entered a relevant link if the position of the mobile object matches to the link of the map data and if it is confirmed from the detection signals of the sensor part that the mobile object has traveled forward for more than a predetermined distance; and detecting an azimuth angle of the mobile object in response to the detection signals of the sensor part and estimating the current position of the mobile object by the dead reckoning navigation if it is discriminated that the mobile object has not entered the link. [0014] Preferably, the azimuth angle of the mobile object is detected by integrating the detection signals of a gyroscope in the sensor part and then accumulating the integrated values. [0015] In accordance with still further aspect of the present invention, there is provided a method of estimating a position of a mobile object in a navigation system comprising the steps of: determining whether the mobile object stops traveling; and backing up a current position data of the mobile object if the mobile object is determined to have stopped. BRIEF DESCRIPTION OF THE DRAWINGS [0016] The above and other objects, features and advantages of the present invention will become apparent from the following description of a preferred embodiment given in conjunction with the accompanying drawings, in which: [0017] FIG. 1 is a block diagram showing a navigation system to which a method of estimating a position of a mobile object according to the present invention is applied; and [0018] FIGS. 2a and 2b are flowcharts illustrating a preferred embodiment of a method of estimating a position of a mobile object according to the present invention. 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